The Battlelog official twitter account announced a little while ago that:

"The current Battlefield 3 and Battlelog outages are a result of activity that appears to be aimed at overwhelming our servers."

"We are working on a variety of solutions to address this problem and are focused on resolution as quickly as possible."

"We will provide the most up to date information to the community on various channels, including the Battlelog twitter account."

"We are very disappointed by these activities and the impact they are having for all to enjoy BF3. Thank you for your patience!"

Sorry it's split up like that, but it's to convey the short twitter posts from @Battlelog :)

Battlelog is not very clear on what they mean by, activity "aimed at overwhelming our servers," however it sounds like some sort of "outsider" is trying to disrupt the normal function of Battlefield 3 and Battlelog. They go on to say they are "very dissapointed." Again, not really sure what they're disappointed with, but it's like they're talking about a child they once had high hopes that has just let them down.

Again, it's not clear on what's causing these problems or what Battlelog meant by their statments. These were just my first thoughts. Whatever the case may be, it looks like DICE and the Battlefield/Battlelog team are on top of it, and are doing everything they can to resolve the issue as quickly as possible.

*UPDATE* DICE has opened a Battlelog thread to keep the Battlefield community up to date on the situation at hand. Latest thread update states:

Despite our security measures, we have been working around the clock to mitigate the impact of an ongoing denial-of-service attack on our Battlefield 3 game infrastructure over the last several days. While the motives are unclear, the focus of the attack has been interference with network communications preventing access to multiplayer gameplay. At this point, no user data is involved. We share your frustration about the impact this has had to our service and the ability for many of you to play Battlefield 3. We are working tirelessly to mitigate the problem.

As a part of our efforts to resolve these issues, we’ve conducted rolling restarts of Battlefield infrastructure servers to apply some updates. Thank you for your patience and support while we work to get everyone back and playing Battlefield 3 as soon as possible. More updates to come.

“The focus of the attack has been interference with network communications preventing access to multiplayer gameplay. At this point, no user data is involved. We share your frustration about the impact this has had to our service and the ability for many of you to play Battlefield 3. We are working tirelessly to mitigate the problem.”
Game servers have been impacted the most, with many people being unable to access the multiplayer, however many people have reported issues with Battlog ranging from being unable to access certain features to stats being completely wiped out. The statement from EA assures us that no "user data is involved," meaning no personal data, and that they "are working tirelessly to mitigate the problem."